[PATCH 1/5] Poison non-POD memset & non-trivially-copyable memcpy/memmove

[Pedro Alves <palves at redhat dot com>]

This patch catches invalid initialization of non-POD types with
memset, at compile time.

This is what I used to catch the problems fixed by the rest of the
series:

  $ make -k 2>&1 | grep "deleted function"
  src/gdb/breakpoint.c:951:53: error: use of deleted function ‘void* memset(T*, int, size_t) [with T = bp_location; <template-parameter-1-2> = void; size_t = long unsigned int]’
  src/gdb/breakpoint.c:7325:32: error: use of deleted function ‘void* memset(T*, int, size_t) [with T = bp_location; <template-parameter-1-2> = void; size_t = long unsigned int]’
  src/gdb/btrace.c:1153:42: error: use of deleted function ‘void* memset(T*, int, size_t) [with T = btrace_insn; <template-parameter-1-2> = void; size_t = long unsigned int]’

I'll move this to the end of the series before pushing (if agreed).

(I've posted another series recently that adds some of the same traits
bits to common/traits.h.  They're really useful.)

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <palves@redhat.com>

	* common/common-defs.h: Include "common/poison.h".
	* common/function-view.h: (Not, Or, Requires): Move to traits.h.
	* common/poison.h: New file.
	* common/traits.h: Include <type_traits>.
	(Not, Or, Requires): New, moved from common/function-view.h.
	(And): New.
---
 gdb/common/common-defs.h   |  1 +
 gdb/common/function-view.h | 40 +++-------------------
 gdb/common/poison.h        | 83 ++++++++++++++++++++++++++++++++++++++++++++++
 gdb/common/traits.h        | 55 ++++++++++++++++++++++++++++++
 4 files changed, 143 insertions(+), 36 deletions(-)
 create mode 100644 gdb/common/poison.h

diff --git a/gdb/common/common-defs.h b/gdb/common/common-defs.h
index af37111..439bce6 100644
--- a/gdb/common/common-defs.h
+++ b/gdb/common/common-defs.h
@@ -82,6 +82,7 @@
 #include "common-debug.h"
 #include "cleanups.h"
 #include "common-exceptions.h"
+#include "common/poison.h"
 
 #define EXTERN_C extern "C"
 #define EXTERN_C_PUSH extern "C" {
diff --git a/gdb/common/function-view.h b/gdb/common/function-view.h
index 66a691b..d4ff2f0 100644
--- a/gdb/common/function-view.h
+++ b/gdb/common/function-view.h
@@ -153,34 +153,6 @@
 
 namespace gdb {
 
-namespace traits {
-  /* A few trait helpers.  */
-  template<typename Predicate>
-  struct Not : public std::integral_constant<bool, !Predicate::value>
-  {};
-
-  template<typename...>
-  struct Or;
-
-  template<>
-  struct Or<> : public std::false_type
-  {};
-
-  template<typename B1>
-  struct Or<B1> : public B1
-  {};
-
-  template<typename B1, typename B2>
-  struct Or<B1, B2>
-    : public std::conditional<B1::value, B1, B2>::type
-  {};
-
-  template<typename B1,typename B2,typename B3, typename... Bn>
-  struct Or<B1, B2, B3, Bn...>
-    : public std::conditional<B1::value, B1, Or<B2, B3, Bn...>>::type
-  {};
-} /* namespace traits */
-
 namespace fv_detail {
 /* Bits shared by all function_view instantiations that do not depend
    on the template parameters.  */
@@ -209,9 +181,9 @@ class function_view<Res (Args...)>
 {
   template<typename From, typename To>
   using CompatibleReturnType
-    = traits::Or<std::is_void<To>,
-		 std::is_same<From, To>,
-		 std::is_convertible<From, To>>;
+    = gdb::Or<std::is_void<To>,
+	      std::is_same<From, To>,
+	      std::is_convertible<From, To>>;
 
   /* True if Func can be called with Args, and either the result is
      Res, convertible to Res or Res is void.  */
@@ -227,10 +199,6 @@ class function_view<Res (Args...)>
     : std::is_same<function_view, typename std::decay<Callable>::type>
   {};
 
-  /* Helper to make SFINAE logic easier to read.  */
-  template<typename Condition>
-  using Requires = typename std::enable_if<Condition::value, void>::type;
-
  public:
 
   /* NULL by default.  */
@@ -248,7 +216,7 @@ class function_view<Res (Args...)>
      compatible.  */
   template
     <typename Callable,
-     typename = Requires<traits::Not<IsFunctionView<Callable>>>,
+     typename = Requires<gdb::Not<IsFunctionView<Callable>>>,
      typename = Requires<IsCompatibleCallable<Callable>>>
   function_view (Callable &&callable) noexcept
   {
diff --git a/gdb/common/poison.h b/gdb/common/poison.h
new file mode 100644
index 0000000..57a1733
--- /dev/null
+++ b/gdb/common/poison.h
@@ -0,0 +1,83 @@
+/* Poison symbols at compile time.
+
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef COMMON_POISON_H
+#define COMMON_POISON_H
+
+#include "traits.h"
+
+/* Poison memset of non-POD types.  The idea is catching invalid
+   initialization of non-POD structs that is easy to be introduced as
+   side effect of refactoring.  For example, say this:
+
+ struct S { VEC(foo_s) *m_data; };
+
+is converted to this at some point:
+
+ struct S {
+   S() { m_data.reserve (10); }
+   std::vector<foo> m_data;
+ };
+
+and old code was initializing B objects like this:
+
+ struct B b;
+ memset (&b, 0, sizeof (B)); // whoops, now wipes vector.
+
+Declaring memset as deleted for non-POD types makes the memset above
+be a compile-time error.  */
+
+/* Helper for SFINAE.  True if "T *" is memsettable.  I.e., if T is
+   either void, or POD.  */
+template<typename T>
+struct IsMemsettable
+  : gdb::Or<std::is_void<T>,
+	    std::is_pod<T>>
+{};
+
+template <typename T,
+	  typename = gdb::Requires<gdb::Not<IsMemsettable<T>>>>
+void *memset (T *s, int c, size_t n) = delete;
+
+/* Similarly, poison memcpy and memmove of non trivially-copyable
+   types, which is undefined.  */
+
+/* True if "T *" is relocatable.  I.e., copyable with memcpy/memmove.
+   I.e., T is either trivially copyable, or void.  */
+template<typename T>
+struct IsRelocatable
+  : gdb::Or<std::is_void<T>,
+	    std::is_trivially_copyable<T>>
+{};
+
+/* True if both source and destination are relocatable.  */
+
+template <typename D, typename S>
+using BothAreRelocatable
+  = gdb::And<IsRelocatable<D>, IsRelocatable<S>>;
+
+template <typename D, typename S,
+	  typename = gdb::Requires<gdb::Not<BothAreRelocatable<D, S>>>>
+void *memcpy (D *dest, const S *src, size_t n) = delete;
+
+template <typename D, typename S,
+	  typename = gdb::Requires<gdb::Not<BothAreRelocatable<D, S>>>>
+void *memmove (D *dest, const S *src, size_t n) = delete;
+
+#endif /* COMMON_POISON_H */
diff --git a/gdb/common/traits.h b/gdb/common/traits.h
index 4b7bac3..1ce2327 100644
--- a/gdb/common/traits.h
+++ b/gdb/common/traits.h
@@ -18,6 +18,8 @@
 #ifndef COMMON_TRAITS_H
 #define COMMON_TRAITS_H
 
+#include <type_traits>
+
 namespace gdb {
 
 /* Pre C++14-safe (CWG 1558) version of C++17's std::void_t.  See
@@ -29,6 +31,59 @@ struct make_void { typedef void type; };
 template<typename... Ts>
 using void_t = typename make_void<Ts...>::type;
 
+/* A few trait helpers, mainly stolen from libstdc++.  Uppercase
+   because "and/or", etc. are reserved keywords.  */
+
+template<typename Predicate>
+struct Not : public std::integral_constant<bool, !Predicate::value>
+{};
+
+template<typename...>
+struct Or;
+
+template<>
+struct Or<> : public std::false_type
+{};
+
+template<typename B1>
+struct Or<B1> : public B1
+{};
+
+template<typename B1, typename B2>
+struct Or<B1, B2>
+  : public std::conditional<B1::value, B1, B2>::type
+{};
+
+template<typename B1,typename B2,typename B3, typename... Bn>
+struct Or<B1, B2, B3, Bn...>
+  : public std::conditional<B1::value, B1, Or<B2, B3, Bn...>>::type
+{};
+
+template<typename...>
+struct And;
+
+template<>
+struct And<> : public std::true_type
+{};
+
+template<typename B1>
+struct And<B1> : public B1
+{};
+
+template<typename B1, typename B2>
+struct And<B1, B2>
+  : public std::conditional<B1::value, B2, B1>::type
+{};
+
+template<typename B1, typename B2, typename B3, typename... Bn>
+struct And<B1, B2, B3, Bn...>
+  : public std::conditional<B1::value, And<B2, B3, Bn...>, B1>::type
+{};
+
+/* Helper to make SFINAE logic easier to read.  */
+template<typename Condition>
+using Requires = typename std::enable_if<Condition::value, void>::type;
+
 }
 
 #endif /* COMMON_TRAITS_H */
-- 
2.5.5